Multiple-cavity mold for producing flash-free parts

ABSTRACT

A means wherein a plurality of mold units, each comprising two or more stacked mold bodies, each of which is held and positioned by a carrier plate in coaxial relation to the other mold bodies. The carrier plates permitting limited axial movement of the mold bodies, thereby to permit stacking of the mold bodies in abutting relation irrespective of difference in lengths of the mold units due to manufacturing tolerance. Each uppermost mold body being exposed to the molding material so that the force thereof presses all of the mold bodies of each mold unit into flash free relations.

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ABSTRACT: A means wherein a plurality of mold units, each e d .h H m I.l 0 mumm [0 31.. te f m 0 HO t m l wm 05d w r epe g two or more stackedmold bodies, each of which is sitioned by a carrier plate in coaxialrelation t odies. The carrier plates permitting limited axial f the moldbodies, thereby to permit stacking of dies in abutting relationirrespective of difference hs of the mold units due to manufactu Eachuppermost mold body bein material so that the force thereof bodies ofeach mold unit into flash fre 0 mw m .m o 5 0 6M n mo P remn md v e odmchomm'm mm n m wn fmfl U l 9 MM DMN M 28 2M 8 .wm

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' PATENTEDJUL20197| SHEET 2 BF 2 INVENTOR- 505557 W 0646 A ffdf/VE V5MULTIPLE-CAVITY MOLD FORPRODUCING FLASH- FREE PARTS BACKGROUND OF THEINVENTION This invention. relates to the art of multiple moldingrubberor rubberlike elastomers aswell as-plastic parts; more particularly,multiple molding wherein theparts of each mold unit are mounted in astacked series, of: carrier plates, rather than formed integrally withina mold-block.

Dueto the fact that it is virtually impossible to make all moldunits ofamolding assem,bly, particularly if each mold unit comprises severalstackedparts, so that they are precisely the same length, it isvirtually impossible to' produce parts which are flash free if attemptis-made tomold more than one part at a, time.

This problem is compoundedias thenumber of moldunits are increased. Ithas heretofor beenthe. practice to circumvent theproblem by producingtheparts with flash,.thentrimming the flash or tumbling the'parts. This, ofcourse, is a second operation which adds to the cost of manufacture.

The purpose of this invention is-to solve this problem so that a largenumber of parts, each requiring pluralityof stacked mold elements, maybe producedaflash'free, therefor the objects of this invention include:I

First, to provide a mold assembly having a large number of mold units,each having several moldbodies, and a stacked series of plates forretaining the mold bodies inproper axial relation, yet allowing limitedaxialmovementof the mold.bodies to compensatefordifferences.in.-axial=,length; Thus, in'effect, each mold unitbehaves just asrifribwerethe-only mold unit in the assembly.

Second, to provide a multiple-unit mold assembly .wherein one oftheendmoldbodiesisfixed-in its carrier'by a cement after its correct positionis established.

Third, to provide a mold assembly whereby a largenumber of mold units,each having several parts, may be incorporated in themold assembly,andwherein any of.the;mold units may be removed orreplacedwithout;disturbing others.

DESCRIPTION OFIDRAWINGS FIG. 1 is a fragmentary viewof-themultiple-cavity mold, with the parts shown in theiriseparatedcondition,-- and with portions shown in section, and other portionsshown in side elevation.

FIG. 2 is a similar fragmentary view of the multiple-cavity mold,partially in section and .partially. in-elevation, .with the parts shownin their. closed orcasting osition.

FIG. 3 is an enlarged fragmentary top. view, taken from33 of FIG. 1.

FIG. 4 and FIG. 5 are enlarged fragmentary sectional views, taken withincircle 4 and circle'5 of FIG. I, and. indicating mold units of differentlengths.

FIG.= 6 is an enlarged fragmentary sectional view, taken within circle 6of FIG. 2.

FIG. 7 is an enlarged fragmentary sectional view,confined principally toone mold unit, and taken through 7-7 of FIG. 3,

the parts of the mold unit being shown in their closed or cast-- ingposition.

FIG. 8 isa similar enlarged. fragmentary sectionalview, showing,themoldunits in their separated condition.

Theqmultiple-cavity mold hereinoillustrated -comprises a multiplicity ofmold units, each .divided:into four=mold parts. Each mold part is heldin a retainer." While four'mold parts are illustrated, it should beunderstood that a lesser or:greater numberof mold parts may be employed.

Themold structure is installed between a conventional bottom platen 1and top platen 2. The parts of the mold units are supported by a firstor bottom carrier plate 3, a second carrier plate 4, a third carrierplate 5, andafourth or top carrier plate 6. The top carrier plate .isprovided-.witha chargereceiving cavity 7 and the top platen is providedwith a plunger 8 which descends into the charge-receiving cavity 7.

Outside the region containing the mold units, the bottom carrier plate 3is provided with tapered centering pins 9, which fit into taperedbushings 10, 11 and 12, provided respectively in the plates 4, Sand 6.

The mold carrier plates 3, 4, 5 and 6 have respectively, axially alignedsets of mold-receiving bores l3, 14, 15 and 16. The bores receive,respectively, mold unit bodies orparts 17, 18; 19 and 20.

Eachmold unit body or part is provided with an enlarged end 21 whichmay-be located at the top or the bottom of the body, and forms ashoulder 22, which limits axialmovement'of the body in thecorresponding-bore.

Near its end, opposite from-the enlarged end 21, each mold unit bodyexcept the upper body20 is provided with a groove 23 which receivesaretainer ring 24. Axial clearance, as indicated by 25, is provided topermit limited axial movement of each mold unit body.

For purposes of illustration, each mold-unit is shown as formed to casta rubber part, having a relatively complex surface. By way of example,the bottom body or part 17 is in the form of a cylinder, havingan-upstanding recess formingpin 26. The next mold unit body 18isprovided with a screwthreaded bore 27, adapted to cast an externallyscrew- ,threaded portion. The upper end of the mold unit body 18 isprovided with coarse serrations 28, which mold complementary serrations.The nextmold unit body 19 is provided with a bore 29 which is largerthan the bore 27, and is contoured to form a pair of annular groovesseparated by ribs. The upper mold unit body 20 is provided with adepending pin 30, to cast a recess in the molded part, and is providedwith a pair of sprue openings 31.

The mold unit bodies l7, l8, l9 and 20 of each mold unit are adapted tobe stacked with their confronting surfacesin abutting relation. Ideally,the-members of each set of mold bodies should be exactly the samelength. This is, of course, impossible to attain, andin practice aminimal variation in length is tolerated. This manufacturing toleranceis compounded by the fact that several of the bodies are stacked to formthecomplete mold-unit. As a consequence, the position occupied by theupper mold unit body 20 varies, as indicated by a comparison of FIGS; 4and 5.

Operation ofthe multiple cavity mold is as follows:

If a charge of molding material 32 is placed in the cavity 7 and presseddownwardly by the plunger 8, the molding material will-exert a downwardforce on each mold unit which is independent of theforce applied to theothermold units. This force is sufficient to holdthe abutting surfacesof the mold bodies infirm, flash free contact. .It should be noted thatif concentricity tolerances permit, the mold bodies may havefree-sliding fit-in their respective bores; otherwise, the fit may be atight press fit which will permit the necessary axial displacement -inresponse to the force exerted on the area of each mold unit. A tightpress fit is avoided not only because of the need foraxial'displacement, but also because of the resulting tendency of thecarrier plates to warp.

Whatever molding material may be used, it is in a highly fluidstate-while it is filling the mold cavities. Consequently, leakage willoccur around the members of the upper set of moldbodies. This is readilyavoided by placing a bonding resin 33 in the spacebetween each mold unitbody 20 and its bore 16, as indicated in FIGS. 7 and'8. A number ofmaterials are suitableyhowever, a curable epoxy resin has been found tobe satisfactory-Before the resin has set, a disc of yieldable plasticmaterial'34, having a higher softening temperature than the moldingmaterial, is substituted for the charge of molding material 32.Polytetrafluoroethylene has been found satisfactory. The molding pressis closed and pressure applied to the plastic disc 34 and heat isapplied through the platens to cause the resin 33 to set, locking eachupper mold unit body 20in its proper position to compensate for anyvariation in length of the mold unit.

The plastic disc is then removed and the multiple-cavity mold is incondition for use. Tests have demonstrated that any desired number ofmold units may be employed and that each will cast a product which willbe entirely free offlash. It will be noted that no loads are applied tothe carrier plates which would cause the plates to warp, so thatexceptionally long runs may be obtained without further adjustment.Should a flash condition occur, it is merely necessary to press themisplaced mold unit body 20 from its bore, replace with bonding resin,reinsert a plastic disc 34, and apply pressure until the resin has set.

While the members of the lowermost set of mold bodies are independent ofeach other, this set may be formed in a single block and only the moldbodies above need be separate from each other and retained by carrierplates.

While particular embodiments of this invention have been shown anddescribed, it is not intended to limit the same to the details of theconstructions set forth, but instead, the invention embraces suchchanges, modifications and equivalents of the various parts and theirrelationships as come within the purview of the appended claims.

lclaim:

l. A multiple-cavity mold structure adapted to be disposed between anupper and a lower platen, the upper platen having a plunger, said moldstructure comprising:

a. a plurality of mold units including an upper set of mold bodies and alower set of mold bodies, each mold unit forming a mold cavity andhaving sprue opening entering the upper end of its upper mold body;

b. a lower carrier having a set of bores slidably receiving said lowerset of mold bodies;

c. means limiting upward movement of said lower set of mold bodies withrespect to said lower carrier;

d. an upper carrier having a cylinder to receive said plunger and acharge of molding material and terminating in a' bottom wall; said uppercarrier also having a set of bores intersecting said bottom wall andslidably receiving said upper set of mold bodies;

. means for limiting upward movement of said upper set of mold bodies;

f. said means for limiting upward movement of said upper set of moldbodies comprising a sealing and bonding material interposed between theupper carrier and the members of said set of upper mold bodies to securesaid upper mold bodies in mold unit length compensating positions;

g. the members of said upper set of mold bodies, when in moldingposition, being exposed to the force exerted by said molding materialupon being pressed by said plunger, and clear of the upward movementlimiting means, each member of said upper set of mold bodies is forcedindividually toward and is limited in its movement by its mating lowermold body irrespective of variations in length ofsaid mold units;

h. said carriers being connected with said platens to effect separationof said mold units on separation of said platens.

2. A multiple-cavity mold structure adapted to be disposed between anupper and a lower platen, the upper platen having a plunger, said moldstructure comprising:

a. a plurality of mold units each including an upper set of mold bodies,a lower set of mold bodies, and at least one set ofintermediate moldbodies, each mold unit forming a mold cavity, and having a sprue openingcommunicating therewith throughout its upper mold body;

carriers for said sets of mold bodies including bores slidably receivingsaid mold bodies;

. means for limiting axial movement of said mold bodies with respect tosaid carriers;

. a cylinder for receiving said plunger and a charge of moldingmaterial, the upper carrier closing the lower end of said cylinder andthe ends of the upper set of mold bodies being exposed to said moldingmaterial and subject to the force exerted thereby when said material ispressed by said plunger;

. a sealing and bonding material interposed between the upper set ofmold bodies and said upper carrier to fix the members of said upper setof mold bodies in their various positions relative to said uppercarrier;

f. each mold unit, when in molding position, being supportedindividually from said lower platen and the members thereof being inabutting relation, the upper mold bodies projecting different distancesinto the cavity formed by said cylinder an upper carrier in accordancewith differences in the lengths of said mold units;

g. said carriers being connected with said platens to effect separationof said mold units on separation of said platens.

3. A multiple-cavity mold structure adapted to be disposed between anupper and a lower platen, the upper platen having a plunger, said moldstructure comprising:

a. a plurality of mold units including at least an upper set of moldbodies and a lower set of mold bodies, said sets varying in length dueto manufacturing tolerances, and the members of said upper set of bodieshaving sprue openings;

. means for holding the bodies of each mold unit in coaxial relation,said means permitting limited axial movement of at least said upper setof mold bodies, whereby said mold bodies may stack in abutting relationirrespective of differences in cumulative length of said mold units;

c. bonding material for securing said upper set of mold bodies inpositions compensating for differences in length ofsaid mold units;

d. means common to said mold units for receiving a charge of moldingmaterial, each member of the upper set of mold bodies being exposedthereto; whereby the mold bodies of each set are forced by said moldingmaterial into material contact irrespective of said differences inlength of said mold units.

1. A multiple-cavity mold structure adapted to be disposed between anupper and a lower platen, the upper platen having a plunger, said moldstructure comprising: a. a plurality of mold units including an upperset of mold bodies and a lower set of mold bodies, each mold unitforming a mold cavity and having sprue opening entering the upper end ofits upper mold body; b. a lower carrier having a set of bores slidablyreceiving said lower set of mold bodies; c. means limiting upwardmovement of said lower set of mold bodies with respect to said lowercarrier; d. an upper carrier having a cylinder to receive said plungerand a charge of molding material and terminating in a bottom wall; saidupper carrier also having a set of bores intersecting said bottom walland slidably receiving said upper set of mold bodies; e. means forlimiting upward movement of said upper set of mold bodies; f. said meansfor limiting upward movement of said upper set of mold bodies comprisinga sealing and bonding material interposed between the upper carrier andthe members of said set of upper mold bodies to secure said upper moldbodies in mold unit length compensating positions; g. the members ofsaid upper set of mold bodies, when in molding position, being exposedto the force exerted by said molding material upon being pressed by saidplunger, and clear of the upward movement limiting means, each member ofsaid upper set of mold bodies is forced individually toward and islimited in its movement by its mating lower mold body irrespective ofvariations in length of said mold units; h. said carriers beingconnected with said platens to effect separation of said mOld units onseparation of said platens.
 2. A multiple-cavity mold structure adaptedto be disposed between an upper and a lower platen, the upper platenhaving a plunger, said mold structure comprising: a. a plurality of moldunits each including an upper set of mold bodies, a lower set of moldbodies, and at least one set of intermediate mold bodies, each mold unitforming a mold cavity, and having a sprue opening communicatingtherewith throughout its upper mold body; b. carriers for said sets ofmold bodies including bores slidably receiving said mold bodies; c.means for limiting axial movement of said mold bodies with respect tosaid carriers; d. a cylinder for receiving said plunger and a charge ofmolding material, the upper carrier closing the lower end of saidcylinder and the ends of the upper set of mold bodies being exposed tosaid molding material and subject to the force exerted thereby when saidmaterial is pressed by said plunger; e. a sealing and bonding materialinterposed between the upper set of mold bodies and said upper carrierto fix the members of said upper set of mold bodies in their variouspositions relative to said upper carrier; f. each mold unit, when inmolding position, being supported individually from said lower platenand the members thereof being in abutting relation, the upper moldbodies projecting different distances into the cavity formed by saidcylinder an upper carrier in accordance with differences in the lengthsof said mold units; g. said carriers being connected with said platensto effect separation of said mold units on separation of said platens.3. A multiple-cavity mold structure adapted to be disposed between anupper and a lower platen, the upper platen having a plunger, said moldstructure comprising: a. a plurality of mold units including at least anupper set of mold bodies and a lower set of mold bodies, said setsvarying in length due to manufacturing tolerances, and the members ofsaid upper set of bodies having sprue openings; b. means for holding thebodies of each mold unit in coaxial relation, said means permittinglimited axial movement of at least said upper set of mold bodies,whereby said mold bodies may stack in abutting relation irrespective ofdifferences in cumulative length of said mold units; c. bonding materialfor securing said upper set of mold bodies in positions compensating fordifferences in length of said mold units; d. means common to said moldunits for receiving a charge of molding material, each member of theupper set of mold bodies being exposed thereto; whereby the mold bodiesof each set are forced by said molding material into material contactirrespective of said differences in length of said mold units.